Low power electromagnetic pump having internal compliant element

ABSTRACT

An electromagnetic pump having a pump body having a fluid containing interior and an inlet and outlet. An accumulator positioned in the fluid containing interior and in fluid communication with the inlet and outlet of the pump. The pump also comprising an armature comprising a pole portion joined to a plunger portion, wherein the plunger portion comprises a one-piece structure including shaft portions of increasing diameters and a head portion comprising a diameter greater than the shaft portions, the plunger portion and a pole portion located internal to the pump housing for magnetic attraction by an electromagnet means. A retainer element is joined with the plunger portion and a main spring urges on the retainer element to move the plunger thus allowing for a return stoke of the plunger as the pump cycles.

FIELD OF THE INVENTION

This invention relates to the field of low power electromagnetic pumps that, for example, can be used in implantable medical device applications, and more particularly to a new improved low power electromagnetic pump having an internal compliant element.

BACKGROUND

An example of a low power electromagnetic pump provided with an accumulator is found in U.S. Pat. No. 5,797,733 issued Aug. 25, 1988, the disclosure of which is hereby incorporated by reference. This patent shows an outlet tube extending from the pump, with an accumulator attached to the outlet tube and a catheter extending from the accumulator. It has been found to be desirable to incorporate an accumulator in the flow path of a low power electromagnetic pump for several reasons. Such placement of the accumulator allows for both the rapid actuation of the pump and the relative slow delivery of the pumped fluid.

The need for an accumulator in a pump flow system arise out of two somewhat different causes, namely, viscous pressure drops which may severely limit flow, and inertial effects which may cause the flow to continue after the pump stroke is complete. The design of a low power electromagnetic pump of the type shown in U.S. Pat. No. 5,797,733 is such that the pump operates more and more efficiently as the rate of the plunger strokes increases. The magnetic force required to move the plunger needs to be maintained for a short time and the electrical energy required to energize the electromagnetic coil can be minimized. However, it is usually not possible to move fluid rapidly through the entire flow path, that is, from the fluid reservoir to the outlet of the flow system. In implantable drug delivery systems it is generally required that the drug be delivered through a small diameter catheter. High flow rates through a small diameter catheter lead to high viscous pressure drops and impose significant performance limitations on the pumping device. This problem is typically alleviated by installing an accumulator at some point between the pump outlet and the catheter to accept the rapid pump outflow and deliver it slowly to the catheter.

If the catheter or the associated tubing are of larger diameter so that the viscous pressure or orifice drops no longer predominate, then the inertial effects may come into play. The inertia of the flow through the rigid inlet and tubes can be an important factor tending to degrade the accuracy of low power electromagnetic pumps. One way this flow inertia is controlled is by the combination of suitable located orifices and properly chosen catheter and accumulator designs.

The inertial flow problem is aggravated in a pump of the type shown in U.S. Pat. No. 5,797,733, due to the long length of the rigid outlet tube located between the pump and the accumulator. The length of this outlet tube was determined not by the performance requirements of the flow system, but rather by the need to bend the tubing as it was being installed in a particular device. Reducing the diameter of the particular tubing would have allowed the bending requirement to be met with a shorter length of tubing, but this would have been at the expense of increased inertial and perhaps viscous effects degrading the pump accuracy.

The benefits of reduction of inertial flow and rapid pull-in can be retained even with a long outlet tube of small inner diameter (for flexibility) if the accumulator can be placed between the pump and the outlet tube. This normally requires that the accumulator be hermetically isolated from the environment. Most accumulator designs used in hydraulic systems meet that requirement or can be modified to do so. However, simple accumulators used for testing the pump, for example a short length of silicone rubber tubing between the rigid outlet tube and catheter, do not satisfy the hermetic requirement.

Published International Patent Application PCT/US99/13902 discloses a solenoid pump including a titanium aneroid accumulator element installed within a sideport assembly. The sideport assembly is located on an external surface of the pump housing between an exit port of the pump mechanism an a catheter. With the compliant element being installed between the pump and the outlet tube, the flow through the outlet tube can be decoupled from the flow through the pump, thus reducing or eliminating the inertial flow. The outlet tube-may therefore be longer and of smaller diameter as required, thus providing the flexibility desired by the customer without degrading the pump accuracy.

SUMMARY

One aspect of this invention involves the benefits that are derived from an alternative approach which comprises moving the accumulator from the end of the outlet tube to the interior of the pump body. These benefits comprise: a more compact pump assembly; facilitated installation of the pump in implantable medical devices; decreased pump housing size; and a decrease in the number of external parts and components. Additionally, there is the added benefit that the accumulator is protected from the outside environment by the pump body.

Another aspect of the invention involves a low porosity filter at the inlet side of the pump. In particular, on the inlet side of the pump the connecting tubing is usually short enough and of large enough diameter so that the viscous pressure drop through the tubing is not a problem, and a conventional accumulator is not required. However, in some applications it may be desirable to install a low porosity filter on the inlet side, but this filter may be incompatible with high flow rates. In such cases the filter itself, or the structure which supports the filter in the pump housing, are designed so that they flex during the pump stroke so that flow may be delivered rapidly to the pump inlet without passing through the filter. Flow may then pass through the filter more slowly driven by the spring constant of the deformed filter or its supporting structure during the interval between pumping strokes. This is a special type of accumulator in which the total internal volume of the flow system is not changed as the accumulator is emptied and refilled, but the volume change downstream exactly compensates for the volume change upstream.

Thus, the invention encompasses a low power electromagnetic pump having an internal compliant element. The pump has a pump body or housing defining an interior fluid containing region comprising a inlet port and an outlet port that are in fluid communication with one another. Check valve means are operatively associated with the fluid containing region for allowing fluid flow in a direction from the inlet port through the outlet port and blocking fluid flow in a direction from the outlet port through the inlet port. An accumulator is located inside the pump body in the interior fluid containing region and is fluid communication with the inlet port and outlet port. The electromagnet means are carried by the pump body and located external to the interior fluid containing region defined in the pump body. An armature is positioned in the interior fluid containing region of the housing and comprises a pole portion for attraction to the electromagnet means. The armature is movably supported in the housing for movement from a rest position through a forward pumping stroke when the pole portion is attracted by the electromagnet to force fluid out the outlet port and for movement in an opposite direction through a return stroke back to the rest position. There are means defining a magnetic circuit including the electromagnet means and the armature and a gap between the pole portion of the armature and the electromagnet means for moving the armature toward the electromagnet means to close the gap in response to electrical energization of the electromagnet means. The accumulator may comprise a bellows-shape or a diaphragm shape. The inlet filter may also serve as an accumulator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a longitudinal sectional view of a low power electromagnetic pump with an aneroid type (bellows-shaped) accumulator installed in the pump body in accordance with the invention.

FIG. 2 shows a longitudinal sectional view of an embodiment of a low power electromagnetic pump according to the invention comprising a diaphragm type accumulator installed in the pump body.

FIG. 3 shows a longitudinal sectional view of an embodiment of a low power electromagnetic pump according to the invention having an inlet filter mounted between two compliant O-rings in the pump body.

FIG. 4 shows a longitudinal sectional view of a an embodiment of a low power electromagnetic pump according to the invention having an accumulator comprising a bellow-shaped accumulator with a dimple modification.

FIG. 5 is a diagrammatic view of the low power electromagnetic pump having an internal compliant element at the rest stage of pump operation.

FIG. 6 is a diagrammatic view of the low power electromagnetic pump having an internal compliant element showing another stage of the forward stroke of the pump armature.

FIG. 7 is a diagrammatic view of the low power electromagnetic pump having an internal compliant element showing a stage of the forward stroke of the pump armature.

FIG. 8 is a diagrammatic view of the low power electromagnetic pump having an internal compliant element showing the return stroke of the pump armature.

DETAILED DESCRIPTION

FIG. 1 shows a longitudinal sectional view of a low power electromagnetic pump 10 having an internal compliant element 300 according to the invention. One of the purposes of placing the internal compliant element 300 inside the pump body 32 is to allow for rapid pumping operation of the pump 10, and the subsequent slow delivery of the fluid pumped to the outlet port 20. The outlet port 20 may be connected with an appropriate fitting so that it can be connected to a catheter (not shown). The pump 10 may thus be used, for example, in implantable drug delivery systems, although the principles of this invention can be variously applied. Following the description of the pump 10 herein are exemplary comparisons showing the pumping results obtained when the pump 10 does not have an internal compliant element, and when the pump does have the internal compliant element 300. The comparisons show the beneficial effects of the internal compliant 300.

As shown in FIG. 1, the pump 10 comprises a pump housing or pump body 32 which is generally hollow, and defines an interior fluid containing region 12. An inlet ferrule 56 is affixed to the pump body 32. The inlet ferrule 56 defines a fluid receiving chamber 14, and the inlet port 18 leads to the fluid receiving chamber 14. An outlet ferrule 318 is affixed to the pump body 32. A fluid output chamber 16 is in fluid communication with an outlet port 20, and the internal compliant 300 is interposed in the flow path between the fluid output chamber 16 and the outlet port 20. The inlet port 18 and outlet port 20 are in fluid communication with one another via pump 10. Inlet port 18 is adapted to be connected to a source or supply of fluid to be pumped, and outlet port 20 is adapted to be in fluid communication with a location to which fluid is to be pumped. A check valve means 24 operatively associates with the fluid-containing region of pump 10 for allowing fluid flow in a direction from the inlet port 18 through the pump 10 and out through the outlet port 20, while blocking fluid flow in a direction from the outlet port 20 through the pump 10 and out through the inlet port 18. The check valve means 24 is operatively associated with a pump armature 45. Fluid enters the inlet port 18, is pumped through the pump 10 by the armature 45, and exits through the outlet port 20.

As shown in FIG. 1, the pump body 32 contains an accumulator recess 320 for accommodating the internal compliant element 300 therein. The internal compliant element 300 in FIG. 1 is embodied as a bellows-type compliant element 300 and may be embodied as an aneroid-type compliant element 300. The accumulator recess 320 is in fluid communication with a outlet tube 130 located within the pump body 32 and with the fluid output chamber 16. The internal compliant element 300 is positioned in the accumulator recess 320 which is located between and which is in fluid communication with both the outlet tube 130 and the pump outlet port 20. The accumulator recess 320 is closed or sealed from the external environment by a plug or the like. When fluid is pumped, the bellows type compliant element 300, which may be made of a resilient material such as rubber, plastics, springable titanium, and other suitable materials, flexes and controls viscous pressure drops and the inertial effects of the fluid being pumped.

The pump body 32 defines a plurality of chambers in the pump 10. These chambers comprise an armature shaft chamber 124, a main spring retainer chamber 126, a bypass chamber 136, and the accumulator recess 320 in fluid communication with one another. The inlet port 18 is in fluid communication with and leads to the armature shaft chamber 124 which is sized to accommodate the pump armature 45 therein. The armature shaft chamber 124 leads to and is in fluid communication with the main spring retainer chamber 126 the width or cross-section dimension of which is greater than the width or cross-section dimension of the armature shaft chamber 124. The main spring retainer chamber 126 is in fluid communication with and leads to output chamber 16, the width or cross-section dimension of the output chamber 16 being greater than the width or cross-section dimension of the main spring retainer chamber 126. The output chamber 16 leads to outlet tube 130 defined in the pump body 32, and the outlet tube 130 is in fluid communication with the compliant element recess 320 defined in the pump body 32. The compliant element recess 320 is sized to hold the internal compliant element 300 therein, thus allowing the internal compliant element 300 to be in fluid communication with the fluid output chamber 16, outlet tube 130, and outlet port 20. The outlet tube 130 is short. As an illustrative example the length of the outlet tube 130, designated L in FIG. 1, may be about 0.1 inches. The outlet tube 130 defines an outlet orifice 132 that may be, for example, between about 0.005 inches and 0.03 inches in diameter. FIGS. 2 and 3 show other embodiments wherein the length of the outlet tube 130 is greater than that shown in FIG. 1.

A passage or orifice 44 is defined in the housing 32 and leads from the armature shaft chamber 124 to a plug chamber 134. The orifice 44, which may be of small diameter, provides for fluid communication between the armature shaft chamber 124 and the plug chamber 134. The plug chamber 134 leads to and is in fluid communication with a bypass chamber 136. The bypass chamber 136 is in fluid communication with the output chamber 16. These chambers thus provide for a bypass passage in the pump 10

The pump armature 45 comprises a pole portion 48 joined to a plunger portion 59 by inner weld ring 75. The armature 45 plunger portion 59 comprises a first shaft portion 60, a second shaft portion 62 of slightly greater diameter than the first shaft portion 60, a third shaft portion 64 of greater diameter than the second shaft portion 62, and a head portion 66 comprising a diameter many time greater than the diameter of the third shaft portion 64. The plunger portion 59, which might be titanium and/or its alloys and/or biocompatible materials, may machined and/or formed from a piece of plunger stock. The inner weld ring 75 thus joins the head portion 66 of the armature 45 with the pole portion 48 and a shell 108. The shell 108 holds a magnetic body 109, and a vacuum hole 70 is provided in armature head portion 66. During assembly of the pump armature 45 a vacuum is created through the vacuum hole 70 and in the shell 108 to draw the magnetic body 109 against the head portion 66 whereupon the hole is sealed by a plug 71. The body 109 is thus held tightly inside the shell 108 as the armature 45 cycles. The pole portion 48 is thus encased to protect the body 109 against potentially corrosive effects of the fluid being pumped.

The main check valve means 24 shown in FIG. 1 is adjacent the upstream end of the armature shaft chamber 124 and allows fluid from an upstream location, for example a reservoir, to enter the pump 10 when the pump 10 is activated. This is the forward stroke 148 shown FIGS. 6 and 7 which will be described presently. The check valve means 24 comprises a disc shaped body or seat 150 with one surface 152 contacting the inlet ferrule 56 and the opposite surface 153 contacting biasing spring 154. The spring 154 biases against the seat 150 and armature 45. During a forward pumping stroke 148 (FIGS. 6 and 7) the check valve means 24 opens allowing fluid from an upstream location to enter the pump 10.

An electromagnet means 100 is isolated from the fluid being pumped by a plate or diaphragm 110. The plate 110 serves as a barrier to prevent the fluids being pumped from contacting the electromagnet 100 and its parts and components. The electromagnet means 100 is activated cyclically to generate an electromagnetic field to pull the armature 45 towards which draws fluid into the pump 10. When the electromagnet means 100 is deactivated, the armature 45 is returned to its at rest state (FIG. 5) by spring 90 in a manner which will be described, and the check valve means 24 closes.

A retainer element 52 having an annular body 54 and a lip portion 55 is provided for the main spring 90 to act against. During assembly, the first and second shaft portions 60, 62 of the armature 45 are fitted through the bore of the retainer element 52, until the retainer element 52 contacts a shoulder 68 formed on the armature 45. The retainer element 52 is joined to the second shaft portion 62 by welding/laser welding and/or friction fitting.

A retainer plate 80 is provided, having a bypass fluid chamber opening 82, an outlet opening 84, and a central opening 86. The central opening 86 is sized to receive the third plunger shaft portion 64 therein, as shown in FIG. 1. The retainer plate 80 also comprises an annular flange 88 surrounding the central opening 86. When the pump is assembled one end 91 of the main spring 90 abuts the lip portion 55 of the retainer element 52, and the opposite end 92 of the main spring 90 abuts against the annular flange 88 of the retainer plate 80.

An outer weld ring 94 comprises an annular support protrusion or lip 95. The retainer plate 80 is positioned between the pump body 32 and the support protrusion 95, and becomes trapped therebetween upon welding the outer weld ring 94. This prevents the movement of the retainer plate 80 as the pump 10 cycles.

The electromagnet means 100 is carried by the pump body 32 and is external to the fluid containing region of the pump body 32. The electromagnet 100 may comprise a core wrapped in a coil and is capable of rapidly energizing and de-energizing to create a magnetic field. This magnetic field then attracts the pole portion 48 of the armature 45. When the pole portion 48 is attracted, the armature 45 compresses the main spring 90 as it moves towards the electromagnet 100. At substantially the same time fluid is drawn into the pump 10. When the electromagnet 100 de-energizes the main spring 90 expands and applies force on the retainer element 52 which moves the armature 45 back to its at rest position in the pump 10 (FIG. 1).

A means for bypass check valving 74 (bypass check valve means) 74 is positioned internal to the pump body 32, between the orifice 44 and a bypass chamber 136. Spring 76 is located between check valve element 78 and a plug 42 mounted to the housing 32 in a plug chamber 134. The bypass check valve means 74 controls fluid communication between the orifice 44 and bypass fluid chamber 136. During the return stroke when the armature 45 returns to its rest position, the bypass check valve means 74 opens. Fluid from the armature shaft chamber 124 flows through the orifice 44 and forces element 78 to open the bypass check valve means 74. The fluid then flows into the bypass chamber 136.

Assembly and Movement of the Armature

During assembly of the armature, the first shaft portion 60, second shaft portion 62, and third shaft portion 64, are moved through the central opening 86 in the spring retainer plate 80 and through the main spring 90. Then, the first and second shaft portions 60,62, respectively, are moved through the retainer element 52 until the retainer element 52 contacts shoulder 68. The retainer element 52 is joined, welded/laser welded, or pressure fitted and welded/laser welded to the second shaft portion 62. The armature 45 is then inserted into the armature shaft chamber 124.

The outer weld ring 94 is moved into the pump body 32 around the retainer plate 80, until the outer weld ring 94 support protrusion 95 and retainer plate 80 contact. The outer weld ring 94 is welded/laser welded to the pump body 32, trapping the retainer plate 80 between the pump body 32 and the support protrusion 95.

For a further and/or more detailed description of the structure of pump 10 and the assembly of the parts thereof, reference may be made to pending U.S. patent application Ser. No. 10/291,130 filed Nov. 8, 2002 and entitled “Low Power Electromagnetic Pump,” now U.S. patent application Publication No. 20030086799 published May 8, 2003, the disclosure of which is hereby incorporated by reference.

Reference is made to the diagrammatic views shown in FIGS. 5-8 which show the cycling of the pump 10:

-   -   a) the pump 10 at rest is shown in FIG. 1 and FIG. 5 (the         electromagnet means 100 is deactivated;     -   b) when the electromagnetic means 100 is activated, a magnetic         circuit comprising the electromagnet means 100 and the armature         45 separated by a gap (designated G in diagrammatic FIGS. 5-8)         is established, and moves the armature 45 toward the         electromagnet means 100 to close the gap, this being a forward         stroke 148;     -   c) during the forward stroke 148 shown in FIGS. 6 and 7, the         check valve 24 opens and fluid enters the pump 10 as indicated         by the fluid inflow arrow 138, the accumulator 300 fills with         fluid, and the armature 45 moves to the left as shown in FIG. 6         in the direction of the arrow designated 140;     -   d) as the forward stroke 148 continues, the main spring 90         compress between the retainer element 52 and the retainer plate         80 as the armature 45 moves toward the electromagnet 100, and         the accumulator 300 continues to amass fluid being pumped and         controllably release the fluid as indicated by the fluid outflow         arrow designated 142 in FIGS. 6 and 7;     -   e) when the gap designated G is substantially closed, the         electromagnet 100 is deactivated and the return stroke 149         follows, as shown in FIG. 8 and indicated by the arrow         designated 144, the main spring 90 moves the armature 45 back to         its at rest position (FIG. 5), and the accumulator 300 continues         to controllably release the fluid being pumped to the outlet         port 20, and from there the fluid exits the pump 10 and may flow         through a catheter or the like; and     -   f) as shown in FIG. 8, during the return stroke 149 the bypass         check valve 74 opens because the fluid between the end 47 of the         armature 45 and check valve 24 becomes pressurized and forces on         check valve element 78, and the fluid flows through orifice 44         and then into the bypass chamber 136, as indicated by the arrow         designated 146, thus allowing the armature 45 to return to its         rest position.

The above-described pumping cycle can be repeated at predetermined intervals. It is noted that the closed check valve 24 during the return stroke 149 prevents fluid from exiting the inlet port 18. Also, the following structure for the pump is for illustrative purposes, and the installation of the internal compliant 300 will work with pumps embodied with different internal structure.

Calculated Results

Compliance may be related to how a fluid path, as defined by the structural body forming the path or part of the path, expands, contracts or deflects under an environmental input, such as, for example, a pressure load from a pump mechanism that is intended to deliver an amount of fluid to an output component, for example a catheter.

One of the purposes of the internal compliant element 300 is to allow for rapid pumping of the pump 10, and the subsequent slow delivery of the fluid pumped to the outlet port 20, and then to, for example, a catheter. Another of the purposes of the internal compliant element 300 is to reduce inertial effects of the fluid being pumped, as such inertial effects can interfere with the smooth operation of the pump 10 and may cause delivery problems.

The following results compare the calculated fluid volume delivered by a pump 10 having an internal compliant element with a pump where the compliant element is located external to the pump body at the end of an outlet tube. A primary basis for the comparison is the percentage reduction in the pulse volume when the back pressure is increased from 0 (zero) pounds per square inch (hereinafter psi) to 10 (ten) psi. A typical performance specification for a pump of the type shown in the above-referenced U.S. Pat. No. 5,797,733 allows for about a 10% decrease in pulse volume when the outlet pressure is increased by 10 psi.

The two basic configurations compared are:

-   -   1) a pump having an outlet tube with an effective length of 3.46         inches with an outlet orifice of 0.005 inch, 0.009 inch, or 0.03         inch diameter located upstream of the end of the outlet tube         with a compliant element located at the end of the outlet tube         (compliant element external to pump body and at end of outlet         tube); and     -   2) a pump having an outlet tube 130 (located internally within         the pump body 32) that is 0.1 inch in length with any of the         same three outlet orifices (0.005 inch, 0.009 inch, or 0.03 inch         in diameter), and a compliant element located at the end of the         internal outlet tube and within the pump housing 32. This second         configuration is intended to represent the effect of moving the         compliant element and outlet orifice to a location within the         pump body 32 in accordance with the invention.

An orifice located downstream of the compliant element would not limit the speed of the pump armature 45 or the volume of internal flow. It is further noted that both configurations are also assumed to incorporate a bypass orifice 44 to help control the inertial flow at the end of the armature 45 stroke.

The 3.46 inch effective length outlet tube used in this calculation is intended to represent an actual outlet tube 2.57 inches long terminated by an outlet fitting. Since the outlet fitting is assumed to be of smaller inner diameter than the outlet tube, the inertial effective length of the outlet tube is increased by the fitting by an amount greater than the physical length of the outlet fitting.

The results are believed accurate enough to provide a useful estimate of the effects.

Table 1 shows the calculated results for a representative configuration of a low power electromagnetic pump with an external accumulator similar to that shown in U.S. Pat. No. 5,9979,733. Although values for leakage through the armature pump body clearance and for the inertial flow were calculated they are omitted from the tabulated results.

The results shown incorporate the calculated magnetic force on the armature, the drag of the pole button as it moves through the pump body and approaches the diaphragm face, the inertia of the plunger, the inertia of the flow upstream of the pump and downstream of the pump outlet, pressure drops in the main flow, bypass circuit and outlet tube caused by check valves, viscosity and orifice restrictions, leakage of fluid through the between the pump body and armature, the increase in pressure in the accumulator during the pumping pulse.

For the external accumulator, the outlet tube has a length of 2.6 inches. The effective outlet tube length with outlet fitting is 3.46 inches. Table 1 shows the calculated results for an external accumulator with the effective length of outlet tube being 3.46 inches. It is noted that in the table the phrase “pounds per square inch” has been abbreviated to PSI in the tables. TABLE 1 Calculated Pulse Volumes for a Pump With An External Accumulator Accumulator Compliance 0.005 0.009 0.03 (micro inch inch inch liter)/PSI ΔP(PSI) orifice orifice orifice Pulse Volume Delivered (μL) 0.03 0.0 0.4896 0.5088 0.5515 10.0 0.4405 0.4768 0.4934 Pulse Volume (10 PSI)/ Pulse Volume (0 PSI) 0.900 0.937 0.895 Pulse Volume Delivered (μL) 0.10 0.0 0.505 0.5541 0.5929 10.0 0.4828 0.5045 0.5397 Pulse Volume (10 PSI)/ PulseVolume (0 PSI) 0.956 0.910 0.910 Pulse Volume Delivered (μL) 2.024 0.0 0.5445 (Bubble In Pump Body) 10.0 0.5182 Pulse Volume (10 PSI)/ Pulse Volume (0 PSI) 0.9520

As shown in Table 1, the results for the 0.03 μL/psi accumulator and the 0.005 inch outlet orifice correspond to a pump of the type shown in U.S. Pat. No. 5,797,733 if it is driven by the lower excitation normally used to drive a pump shown in U.S. Pat. No. 6,264,439. The results indicate that under these conditions the armature 45 is not drawn in fully against 10 psi before the capacitor is discharged and the pulse volume against 10 psi is 10% lower than the pulse volume with no pressure increase across the pump 10, a value just meeting the specified performance of the pump. The pulse volume ratio (pulse volume against 10.0 psi divided by the pulse volume against 0 psi) can be improved to 0.956 by increasing the accumulator compliance to 0.1 μL/psi or to 0.937 by increasing the diameter of the outlet orifice to 0.009 inches. If both changes are made the pulse volume ratio is degraded to 0.91 by increased inertial flow.

The third value of compliance listed represents the compliance which would exist if a 50 μL bubble occupied the volume of the pump body 32. It is assumed that there is no air in the pump chamber (between the check valve means 24 and armature 45), because even a small bubble could cause a reduction in pump volume and a decrease in pump accuracy. The use of the 0.03 orifice in this calculation reflects the fact that there is no satisfactory location for an orifice between the armature 45 and the accumulator (bubble) and therefore the effective orifice is large.

Table 1 also shows that pulse volume is reduced from that calculated for the 0.1 μL/psi example. This occurs because the inertia of the fluid in the long outlet tube no longer affects the flow during the pumping pulse. The calculated PV ratio at 10 psi of 0.952 is well above the specified lower limit of 0.9. However, the PV ratio is less meaningful than the ratio of the fluid delivered with the bubble present to the delivery with the bubble in normal operation with no bubble. Against 10 psi with a 0.005 orifice and a 0.1 μL/psi accumulator the ratio is 0.5182/0.4828=1.0735. Thus the pump 10 would deliver greater volume with the bubble within the pump body 32 than it would with no bubble present.

Table 2 shows the results of calculations in which the accumulator 300 is assumed to be internal to the pump body 32. This placement of the accumulator 300 shortens the effective length of the outlet tube and reduces the inertial effect. If necessary an orifice can also be accommodated within the pump body 32 upstream of the accumulator. Results are therefore shown for all three orifice sizes. Since the outlet orifice serves to control the inertia effects of both the inlet and outlet tubes, there may be a benefit from including an orifice even though there is effectively no outlet tube. As in Table 1, a 0.005 inch outlet orifice would slow the armature pull-in to a point where the pull-in would be incomplete at 10 psi with a less compliant accumulator and the calculated PV ratio is an unacceptable 0.894. Increasing the orifice size to 0.03 inch improves the PV ratio at 10 psi to 0.94 with the 0.03 μL/psi accumulator. Note that all three of the orifice sizes and both the accumulator compliances meet the PV ratio accuracy criterion, except for the combination of the smallest (0.005 inch) orifice and the least compliant accumulator (0.03 μL/psi).

Table 2 shows the results of locating a bellows-type accumulator 304 internal to the pump body 32, between the outlet tube 130 and pump outlet port 20, as shown in FIG. 1. For this example, the internal accumulator 304 has an effective outlet tube 130 length of 0.1 inches, and the outlet orifice 132 diameter is any of the following: 0.005 inches; 0.009 inches; and 0.03 inches. The results are presented in Table 2. TABLE 2 Calculated Pulse Volumes for a Pump with an Internal Accumulator Accumulator Compliance 0.005 0.009 0.03 (micro inch inch inch liter)/PSI ΔP(PSI) orifice orifice orifice Pulse Volume Delivered (μL) 0.03 0.0 0.4895 0.5039 0.5118 10.0 0.4376 0.4651 0.4816 Pulse Volume (10 PSI)/ Pulse Volume (0 PSI) 0.8940 0.9230 0.9410 Pulse Volume Delivered (μL) 0.10 0.0 0.5055 0.5185 0.5330 10.0 0.4822 0.5032 0.5081 Pulse Volume (10 PSI)/ Pulse Volume (0 PSI) 0.9540 0.9710 0.9530 Pulse Volume Delivered (μL) 2.024 0.0 0.5445 (Bubble In Pump Body) 10.0 0.5183 Pulse Volume (10 PSI)/ Pulse Volume (0 PSI) 0.9520

There still remains some inertial effect even with an internal accumulator installed in the pump 10. The source of this inertial effect is the inlet tube, which has not been varied in these calculations. Thus, in the example of the 0.1 μL/psi compliant element, which does not control inertial flow as well as the stiffer compliance, a 0.009 inch orifice, as compared with the 0.03 inch orifice, improves the PV ratio from 0.953 to 0.971. However, with the 0.03 μL/psi compliance the pump 10 is more accurate with the larger 0.03 inch orifice.

The effect of a bubble in the body of the pump 10 on the volume delivered against 10 psi is less when the accumulator is internal. As shown in Table 2, the volume delivered with the bubble present is 0.5183 μL. If the accumulator compliance without the bubble is 0.1 μL/psi, then the normal delivered volume is 0.5081 μL so that the effect of the bubble in the pump body is to increase the delivered volume by the ratio 0.5183/0.5081=1.02, that is, by about two percent (2%).

An advantage of placing the accumulator (compliant element) within the pump body 32 is that it reduces or eliminates the effect of the inertial flow and orifice 132 in the outlet tube 130 on the delivered pulse volume, thereby improving the accuracy of the pump 10. If a bubble (not shown) should be trapped within the pump body 32 it also acts as an internal compliant element and changes (while the bubble is present) the delivered volume. Placing the compliant element 300 within the pump body 32 has the effect of reducing the magnitude of the change due to the bubble and assists in maintaining the accuracy of the low power electromagnetic pump 10. Other advantages of placing the compliant internal to the pump body include a more compact pump.

In another embodiment, shown in FIG. 2, the pump 10 comprises a diaphragm-type accumulator 306 mounted therein. The diaphragm-type accumulator 306 functions in substantially the same way as the bellow-shaped accumulator 304, in that it allows for rapid pumping of the pump 10, and the subsequent slow delivery of the fluid pumped to the outlet port 20 and from there to, for example, a catheter. The diaphragm type internal compliant 306 also reduces inertial effects of the fluid being pumped, that can interfere with the smooth operation of the pump 10 and that may cause delivery problems.

Applications arise in which it is desirable to install a low porosity filter on the inlet side of the pump 10, but such filters are incompatible with high flow rates. In such cases the filter itself or the structure which or means for support 305 that supports the filter in the pump housing are designed so that they flex during the pump stroke so that flow may be delivered rapidly to the pump inlet without passing through the filter. O-rings can be used as the means for support along with other suitable structures. Flow may then pass through the filter more slowly driven by the spring constant of the deformed filter or its supporting structure during the interval between pumping strokes. This is a special type of accumulator in which the total internal volume of the flow system is not changed as the accumulator is emptied and refilled, but the volume change downstream exactly compensates for the volume change upstream.

It is to be understood that the diameters of the orifice 132 presented in the Table 2 (0.005, 0.009, and 0.03 inches) are not the only sized orifices available for use in the present invention. The orifice diameter of the outlet tube 130 may be in the range of 0.004 inches to 0.04 inches, and the present invention encompasses all outlet orifices sized in this range. Also, the length of the outlet tube 130 may be about 0.1 inches.

In another embodiment shown in FIG. 3, a combination of a diaphragm-type accumulator 306 and a flexible filter accumulator 308 is shown. The flexible filter accumulator 308 comprises a filter 98 supported in the ferrule 56 by means for support 305. The means for support 305 shown in FIGS. 3 and 4 include O-rings 310, but the means for support 305 may be otherwise embodied. The flexible filter accumulator 308 shown in FIG. 3 is suitable for use in combination with a low porosity filter 98, because it permits slow flow through the filter 98 with rapid with rapid flow through the pump 10.

Another embodiment of the low power electromagnetic pump with internal compliant element 10 is shown in FIG. 4. Here, a bellows-type accumulator 304 is used in combination with a flexible filter accumulator 308. The bellows-type accumulator 304 is provided with dimples 307 on the outer surface of the bellows. These dimples 307 ensure proper communication with the pressure source and the mated surfaces of the outer pillows 309 and center pillow 311 of the accumulator 304. The dimples 307 may, in other embodiments, be replace with plus-shaped spacer (not shown) placed above and below each pillow 309, 311, with the two center spacers shared by adjacent pillows. Other embodiments include a split ring (not shown) that supports the outer edge of each assembly, with its thickness determined by the desired spacing between the pillows.

Thus, it has been shown that the internal compliant element 300 may be variously embodied, all of these within the scope of the present low power electromagnetic pump having an internal compliant element. Also, the performance benefits obtainable by installing an accumulator within the pump body 32 of a low power electromagnetic pump 10 rather than at the end of an external outlet tubing have been calculated, and suitable configurations of the accumulator are shown and described. In addition, an accumulator which does not cause a change in the volume of the flow path has been shown and described. This accumulator is particularly suitable for use in combination with a low porosity filter, since it permits slow flow through the filter and rapid flow through the electromagnetic pump.

It will be appreciated by those skilled in the art that while the low power electromagnetic pump having an internal compliant element has been described in connection with particular embodiments and examples, the low power electromagnetic pump having an internal compliant element is not necessarily so limited and that other examples, uses, modifications, and departures from the embodiments, examples, and uses may be made without departing from the low power electromagnetic pump having an internal compliant element. All these embodiments are intended to be within the scope and spirit of the appended claims. 

1. A low power electromagnetic pump having an internal compliant element comprising: a) a pump body defining an interior fluid containing region comprising a inlet port and an outlet port in fluid communication with one another; b) check valve means operatively associated with the fluid containing region for allowing fluid flow in a direction from the inlet port through the outlet port and blocking fluid flow in a direction from the outlet port through the inlet port; c) an accumulator located inside the pump body in the interior fluid containing region in fluid communication with the inlet port and outlet port; d) electromagnet means carried by the pump body and located external to the interior fluid containing region defined in the pump body; e) an armature positioned in the interior fluid containing region of the pump body, the armature comprising a pole portion for attraction to the electromagnet means; f) the armature being movably supported in the pump body for movement from a rest position through a forward pumping stroke when the pole portion is attracted by the electromagnet to force fluid out the outlet port and for movement in an opposite direction through a return stroke back to the rest position; and g) means defining a magnetic circuit including the electromagnet means and the armature and a gap between the pole portion of the armature and the electromagnet means for moving the armature toward the electromagnet means to close the gap in response to electrical energization of the electromagnet means.
 2. The low power electromagnetic pump having an internal compliant element according to claim 1 wherein the accumulator comprises a bellows-shape
 3. The low power electromagnetic pump having an internal compliant element according to claim 1 wherein the interior fluid containing region comprises a pole button chamber and an outlet tube located internal to the pump body and extending from the pole button chamber to the accumulator such that the accumulator is positioned between the outlet tube and the outlet port.
 4. The low power electromagnetic pump according to claim 3 wherein the outlet tube is about 0.1 inches in length.
 5. The low power electromagnetic pump according to claim 3 wherein the outlet tube comprises an orifice having a diameter in the range of 0.004 inches to 0.04 inches.
 6. The low power electromagnetic pump having an internal compliant element according to claim 1 wherein the accumulator comprises a diaphragm-type accumulator.
 7. The low power electromagnetic pump having an internal compliant element according to claim 6 wherein the interior fluid containing region comprises a pole button chamber and an outlet tube located internal to the pump body and extending from the pole button chamber to the diaphragm-type accumulator such that the diaphragm-type accumulator is positioned between the outlet tube and the outlet port.
 8. The low power electromagnetic pump according to claim 7 wherein the outlet tube is about 0.1 inches in length.
 9. The low power electromagnetic pump according to claim 7 wherein the outlet tube comprises an orifice and the orifice diameter is in the range of 0.004 inches to 0.04 inches in diameter.
 10. A low power electromagnetic pump having an internal compliant element comprising: a) a pump body defining an interior fluid containing region comprising a inlet port and an outlet port in fluid communication with one another; b) check valve means operatively associated with the interior fluid containing region for allowing fluid flow in a direction from the inlet port through the outlet port and blocking fluid flow in a direction from the outlet port through the inlet port; c) an accumulator located inside the pump body in the interior fluid containing region in fluid communication with the inlet port and outlet port; d) a filter supported in the pump body, the filter being in fluid communication with the inlet port and the interior fluid containing region; e) electromagnet means carried by the pump body and located external to the interior fluid containing region defined in the pump body; f) an armature positioned in the interior fluid containing region of the pump body, the armature comprising a pole portion for attraction to the electromagnet means; g) the armature being movably supported in the pump body for movement from a rest position through a forward pumping stroke when the pole portion is attracted by the electromagnet to force fluid out the outlet port and for movement in an opposite direction through a return stroke back to the rest position; and h) means defining a magnetic circuit including the electromagnet means and the armature and a gap between the pole portion of the armature and the electromagnet means for moving the armature toward the electromagnet means to close the gap in response to electrical energization of the electromagnet means.
 11. The low power electromagnetic pump having an internal compliant element according to claim 10 further comprising a ferrule mounted to the pump body and a means for support and wherein the means for support is for supporting the filter in the ferrule.
 12. The low power electromagnetic pump having an internal compliant element according to claim 10 further comprising O-rings positioned in the ferrule for supporting the filter.
 13. The low power electromagnetic pump having an internal compliant element according to claim 10 wherein the accumulator is a diaphragm type accumulator.
 14. The low power electromagnetic pump having an internal compliant element according to claim 10 wherein the accumulator is a bellows type accumulator.
 15. The low power electromagnetic pump having an internal compliant element according to claim 10 wherein the interior fluid containing region comprises a pole button chamber and an outlet tube located internal to the pump body and extending from the pole button chamber to the accumulator such that the accumulator is positioned between the outlet tube and the outlet port.
 16. The low power electromagnetic pump according to claim 15 wherein the outlet tube is about 0.1 inches in length.
 17. The low power electromagnetic pump according to claim 15 wherein the outlet tube comprises an orifice and the orifice is in the range of 0.004 inches to 0.04 inches in diameter.
 18. A low power electromagnetic pump comprising: a) a pump body comprising an inlet port and an outlet port in fluid communication with one another; b) the pump body defining an interior fluid container region comprising an armature shaft chamber which is in fluid communication with the inlet port, and further comprising a pole button chamber that is in fluid communication with the armature shaft chamber; c) an armature comprising a pole portion and a plunger portion positioned in the armature shaft chamber; d) an accumulator positioned in the interior fluid containing region and located between the inlet port and the outlet port; and e) an electromagnet for energizing and generating an electromagnetic field to attract and move the pole button of the armature from a rest position through the forward pumping stroke, and for de-energizing allowing the armature to return the rest position.
 19. The low power electromagnetic pump according to claim 18 further comprising an outlet tube and an accumulator recess in the pump body for receiving the accumulator and wherein the outlet tube leads from the pole button recess to the accumulator recess and wherein the accumulator recess leads to the outlet port.
 20. The low power electromagnetic pump according to claim 18 wherein the accumulator is one of the following: a diaphragm type accumulator, a bellows type accumulator, or a bellows type accumulator wherein the bellows are separated by dimples.
 21. The low power electromagnetic pump according to claim 18 further comprising a filter supported in the pump body and in fluid communication with the inlet port and the interior fluid containing region.
 22. The low power electromagnetic pump according to claim 21 further comprising a ferrule mounted to the pump body and a means for support positioned in the ferrule and wherein the means for support is for supporting the filter in the ferrule.
 23. The low power electromagnetic pump according to claim 22 wherein the means for support comprise O-rings.
 24. The low power electromagnetic pump according to claim 19 wherein the outlet tube is about 0.1 inches in length.
 25. The low power electromagnetic pump according to claim 19 wherein the outlet tube comprises an orifice having a diameter in the range of 0.004 inches to 0.04 inches.
 26. A method of pumping with a low power electromagnetic pump having an internal compliant element comprising: a) providing a pump body defining an interior fluid containing region in the pump body, and providing the pump body with an inlet port and an outlet port in fluid communication with one another; b) providing check valve means operatively associated with the fluid containing region for allowing fluid flow in a direction from the inlet port through the outlet port and blocking fluid flow in a direction from the outlet port through the inlet port; c) placing an accumulator inside the pump body fluid and providing fluid communication between the interior fluid containing region, the accumulator, the inlet port, and the outlet port; d) providing electromagnet means associated with the pump body and locating it external to the interior fluid containing region defined in the pump body; e) locating an armature in the interior fluid containing region of the pump body, the armature comprising a pole portion for attraction to the electromagnet means; f) supporting the armature in the pump body and moving it from a rest position through a forward pumping stroke when the pole portion is attracted by the electromagnet to force fluid out the outlet port and moving the armature in an opposite direction through a return stroke back to the rest position; g) providing means defining a magnetic circuit including the electromagnet means and the armature and a gap between the pole portion of the armature and the electromagnet means for moving the armature toward the electromagnet means to close the gap in response to electrical energization of the electromagnet means; and h) utilizing the accumulator to allow rapid pumping operation of the pump and subsequent slow delivery of fluid to the outlet port.
 27. A method according to claim 26, further includes providing a filter in fluid communication with the inlet port and interior fluid containing region. 